Aluminum based alloy bearing

ABSTRACT

IN A PREFERRED EMBODIMENT A CAST STRIP OF ALUMINUM BEARING ALLOY CONTAINING A MINOR PORTION OF LEAD DISPERSED AS SMALL SPHERICAL PARTICLES IN THE ALUMINUM MATRIX IS ROLLED LENGTHWISE, WHEREBY THE SOFT LEAD PARTICLES ARE FLATTENED AND LENGTHENED IN THE DIRECTION OF ROLLING. SLEEVE BEARING BLANKS ARE THEN CUT FROM THE CAST AND ROLLED STRIP IN A DIRECTION AND MANNER SUCH THAT THE LONGEST DIMENSION OF THE FLATTENED LEAD PARTICLES IN THE FINISHED BEARING IS TRANSVERSE TO THE INTENDED DIRECTION OF ROTATION OF A MATING JOURNAL MEMBER.

June 6, 1972 E41. WEBBERE ALUMINUM BASED ALLOY BEARING Original Filed05:. 29, 1968 DIRECTION OF JOURNAL MOTION IIIIIII'IIIIIm DIRECTION OFROLLING Fig.4

INVENTOR fi ed Il/ebbere %u7 d. M ATTORNEY United States Patent3,667,823 ALUMINUM BASED ALLOY BEARING Fred J. Webbere, Orchard Lake,Mich., assignor to General Motors Corporation, Detroit, Mich. Originalapplication Oct. 29, 1968, Ser. No. 771,416, now Patent No. 3,562,884,dated Feb. 16, 1971. Divided and this application Aug. 10, 1970, Ser.No. 62,391 Int. Cl. F16c 33/12 U.S. Cl. 308237 6 Claims ABSTRACT OF THEDISCLOSURE In a preferred embodiment a cast strip of aluminum bearingalloy containing a minor portion of lead dispersed as small sphericalparticles in the aluminum matrix is rolled lengthwise, whereby the softlead particles are flattened and lengthened in the direction of rolling.Sleeve bearing blanks are then cut from the cast and rolled strip in adirection and manner such that the longest dimension of the flattenedlead particles in the finished bearing is transverse to the intendeddirection of rotation of a mating journal member.

This is a division of Ser. No. 771,416, filed Oct. 29, 1968, now Pat.No. 3,562,884, issued Feb. 16, 1971.

This invention relates to the processing of aluminum based bearingmaterial suitable for sleeve bearings and the like. More particularly,this invention relates to aluminum bearing alloys containing a dispersedphase of soft metal and to a method of processing such alloys wherebythe soft phase is formed into generally fiat elongated plateletssubstantially parallel to the bearing surface. The orientation of theplatelets in the finished bearing member is arranged and controlled toprovide the most advantageous exposure of the soft phase with respect tobearing operation.

In U.S. Pat. No. 3,410,331, issued Nov. 12, 1968, entitled Method ofCasting an Aluminum Based Bearing Alloy and assigned to the assignee ofthe subject invention, a method is disclosed for forming a cast bearingalloy containing generally spherical particles of lead dispersed in analuminum matrix. In accordance with the teachings of the aforesaidpatent, a strip of lead containing aluminum based alloy is cast in amanner whereby the concentration of lead increases in a direction fromone surface of the strip to the opposite surface. This previous patent,Pat. No. 3,410,331, which is incorporated by reference herein, teachesthat the dispersion of minute lead particles in an aluminum matrixprovides an excellent bearing material particularly for use in sleevebearings and the like. 'In general, the cast aluminum strip iseventually bonded to a steel backing strip for support, the low leadconcentration side of the aluminum strip being bonded to the steelbacking and the high lead concentration side of the aluminum stripbecoming the bearing surface. Bearing materials of the describedcomposition and structure provide excellent bearing properties due tothe dispersion of the lead babbitt in the aluminum matrix. In fact,sleeve bearings of this type have been found to have properties equal toor superior to the same properties of more expensive lead-free aluminumalloy sleeve bearings which are provided with an overplate of babbittmetal.

It is an object of the present invention to provide an improved methodof processing a cast aluminum based bearing alloy, containing adispersion of a suitable soft metal, to place the dispersed soft metalin a form having maximum surface exposure of the soft phase for thepurpose of optimizing the properties of the bearing material.

It is another object of the present invention to provide an aluminumbased bearing material containing therein a dispersion of a soft metal,such as lead or other babbitt metal, wherein the dispersed soft metal isin a specific coufiguration and orientation which offers the optimumexposure thereof at a bearing surface from the standpoint of improvedscore resistance and embedability of foreign particles.

In accordance with a preferred embodiment of my invention, these andother objects are accomplished by first providing a cast strip ofaluminum based alloy having incorporated therein a dispersed phase offinely divided, generally spherically shaped lead particles. In general,it is preferred that the cast strip be formed in accordance with theteachings of the above-identified Pat. No. 3,410,331 so that the leadconcentration increases in a direction from one of the principalsurfaces of the cast strip to the other. The cast strip is milled,machined or otherwise trimmed to a suitable predetermined dimension andthen rolled to obtain a reduction in thickness and, when desired, tobond the cast aluminum alloy strip to a suitable backing material suchas steel. The cast strip is preferably rolled lengthwise. Besidesobtaining a reduction in the thickness of the strip by the rollingoperation the spherical lead particles are flattened and, in some casesfragmented and converted for the most part into flat platelets in thealuminum matrix. The thin dimension of each platelet is roughlyperpendicular to the rolled surface. The broad dimensions of a majorportion of the platelets lie in or parallel to the plane of the workingsurface of the bearing material. The cast and rolled strip is cut intobearing blanks which are processed by conventional forming and machiningoperations into bearings, such as plain sleeve bearings. However, inaccordance with my invention the cutting or shearing of the blanks fromthe main strip is undertaken in a direction and manner so that thelongest dimension of the soft metal platelets in the finished bearingwill lie transverse to the intended direction of rotation of a matingjournal member or the like. In other words, the intended direction ofrotation of a journal member with respect to the finished bearingmaterial is transverse to the direction in which the bearing materialwas originally rolled. In this way the flat elongated soft particles liecrossways to the movement of the journal to provide the maximum exposedarea and opportunity for embedding foreign particles entrained betweenthe rotating journal and the bearing surface and to scoring of thebearing surface.

These and other objects and advantages of my invention wiH become moreapparent from a detailed description thereof, reference being bad to theattached drawings in which:

FIG. 1 is a perspective view of a roll bonded bimetal strip ofaluminum-soft metal alloy backed with steel;

FIG. 2 is a perspective view of a bimetal sleeve hearing formed from ablank sheared from the strip of FIG. 1 in the manner indicated;

FIG. 3 is a photomicrograph at x of a portion of the aluminum alloysurface of the roll bonded strip of FIG. 1;

FIG. 4 is a photomicrograph at 100x of a section of the bimetal strip ofFIG. I, viewed from the side; and

FIG. 5 is a photomicrograph at 100x of a section of the bimetal strip ofFIG. 1, viewed endwise.

In the following detailed description of a preferred manner ofpracticing my invention, reference is made to the use of analuminum-lead alloy prepared in accordance with the above-identifiedPat. No. 3,410,331, which is eventually roll bonded to a steel backing.It will be recognized, however, that my invention is equally applicableto aluminum alloys containing soft metals other than ice lead, such ascadmium or bismuth, and which are not necessarily provided with abacking layer.

Molten alloy was prepared in an induction heating furnace, the alloycomprising by weight about 4.75% lead, 0.5% tin, 4% silicon, 1% cadmium,0.10% magnesium, 0.20% manganese, 0.10% copper and the balance aluminum.After being heated to a temperature of about 1750 F. the molten metalwas caused to flow from the induction furnace into a horizontallydisposed, open ended mold, such as that depicted in FIG. 2 of theabove-identilied patent. The rate of cooling of the metal in the moldwas controlled so that droplets of liquid lead forming in the moltenaluminum were permitted to migrate under the influence of gravity beforethe aluminum completely solidified. In this Way a dispersion of fine,generally spherical particles of lead was found throughout the aluminummatrix but with a gradient in the lead concentration from the top to thebottom of the horizontally cast strip. Because lead is more dense thanaluminum, the concentration of the dispersed lead phase increased in thedirection from the top to the bottom of the cast strip. A microscopicexamination of the cast strip, such as is depicted in FIGS. 3 and 4 ofthe above-identified Pat. No. 3,410,331, clearly shows that thedispersed lead particles are generally spherical in configuration in theas-cast strip.

In this example the open ended mold was arranged and constructed so thatthe cast strip was rectangular in cross section, about inch in thicknessand 5% inches Wide. A small amount of material was milled from both thetop and bottom surfaces to provide a strip having more preciselyparallel surfaces. Sections of cast strip two hundred feet in lengthwere rolled into coils and the coils annealed and stress relieved. Thecoiled and annealed strip, now slightly less than inch in thickness, waspassed repeatedly between suitable rollers whereby the thickness of thestrip was reduced to about 0.050 inch. The strip was not permitted toexpand substantially in width. Therefore, an approximately six-foldelongation was obtained. Subsequent to the last pass between the rollersthe edges of the strip were trimmed so that the width thereof wasequivalent to the intended semicircumferential length of the ultimatesleeve bearing to be produced.

After the rolling and trimming operations the strip of aluminum-babbittmetal alloy was annealed. The rolled and annealed strip was thensuitable for roll bonding with a low-carbon steel backing layer. Thiswas accomplished by preheating a thin steel backing strip ofsubstantially the same width as the aluminum based strip to about 1200"F.; juxtaposing the aluminum strip and the steel strip, the low leadside of the aluminum strip being against the steel strip, and passingthe two strips between suitable rollers. During the roll bondingoperation the aluminum strip underwent a further reduction in thickness,approximately 3 to 1, and became firmly and coextensively bonded to thesteel backing. At this stage the thickness of the aluminum layer in thebimetal strip was about 0.016 inch to 0.018 inch. A perspective viewdepicting a typical section of aluminum bearing material-steel backingbimetal strip is shown in FIG. 1 at 10. The relative thicknesses ofaluminum material 12 and steel backing 14 are not necessarily accuratelyrepresented. As indicated above, the strip was rolled lengthwise in eachinstance so that the dispersed lead particles 16 (with which some tinand cadmium is associated), which are exaggerated in size for purposesof illustration, are flattened and elongated in the direction ofrolling. The photornicrograph of FIG. 3 portrays the fragmented andflattened lead particles 16 in the aluminum matrix. FIG. 4 is aphotomicrograph of a section of the roll bonded bimetal strip as viewedfrom the side, the aluminum based layer 12 being bonded to the steellayer 14. The lead particles 16 at this stage are extremely thin andscarcely visible in marked contrast to the generally spherical shapedparticles in the as-cast alloy, as depicted in FIGS. 3 and 4 of theabove-identified Pat. No. 3,410,331. The thin lead platelets 16 are seento be sub- 4 stantially parallel to the top surface 18 of the aluminumlayer.

FIG. 5 is a photomicrograph of a section taken in a plane perpendicularto the direction of rolling or, in other words, an end view of the rollbonded strip. The lead platelets 16 are seen to be quite thin andgenerally parallel to the exposed upper surface of the aluminum portion.

Bearing blanks are now cut or sheared from the bimetal strip. In thisexample a plain sleeve bearing, illustrated at 20 in FIG. 2, is to beformed and the direction of motion of the mating journal member will beas indicated by the arrow. Accordingly, the bearing blanks are in thisinstance sheared crossways from the bimetal strip. The blanks are formedinto half circle shapes with the aluminum layer 12 being inward of thesteel backup layer 14. At this point any final machining operations areperformed on the bearing which may be necessary to trim the article toits final dimensions.

The soft dispersed lead platelets 16 at the surface of the aluminumlayer and dispersed throughout are shown at FIG. 2 as being aligned withtheir longest dimension perpendicular or transverse with respect to thedirection of rotation of a journal member and the elongated plateletsand fragments of platelets are so oriented that the two major dimensionsthereof are in planes generally parallel to the bearing surface. In thisarrangement the lead babbitt phase provides maximum embedability offoreign particles which typically are entrained between the movingjournal and the bearing surface. This is because any foreign particlesso entrained are moving in a direction cross- Ways to the elongatedplatelets and are much more likely to encounter a soft phase. Moreover,in the arrangement described, the soft lead phase is most effective inincreasing the score resistance of the bearing surface. The describedmethod of processing aluminum-soft metal alloys and particularlyaluminum-lead alloys provides a bearing material offering most of thedesirable properties of the conventional aluminum-silicon-cadmiumbearing alloys having a lead babbitt overplate for score resistance andembedability, but the subject composition is less expensive tomanufacture.

My invention is particularly applicable to cast aluminum-soft metalalloys wherein the soft metal is present as a distinct phase in analuminum matrix. In general, it is necessary and preferred that the softmetal phase be a dispersion of more or less spherical particles in theas-cast condition. In order that this can be achieved there must be asuitable temperature range above the temperature at which aluminumsolidifies wherein the molten soft metal has low solubility in moltenaluminum. Therefore, as the higher melting aluminum solidifies the softmetal is entrained as a separate phase in the aluminum matrix. In apreferred form of the invention the molten soft metal may be caused tomigrate in the molten aluminum to achieve a gradient in theconcentration of the soft metal in the final casting.

Lead, cadmium and bismuth are examples of soft metals which have limitedsolubility in molten aluminum at temperatures just above thesolidification temperature of aluminum. Lead has a maximum solubility ofabout one to two percent by weight in aluminum under these conditions.Bismuth has a maximum solubility of about three percent by Weight ofmolten aluminum, and cadmium forms a separate liquid phase in moltenaluminum (at temperatures just above the melting point of aluminum) whenpresent in quantities greater than about eight to nine percent by weightof the binary mixture. It will be appreciated that the above statedsolubility limits are for the respective aluminum-soft metal binarysystems, and that the presence of other alloying metals may markedlyincrease or decrease these solubility values.

Accordingly, soft metals such as lead, bismuth and cadmium may bealloyed with aluminum and cast into a strip wherein at least some of thesoft metal is dispensed as generally spherical particles in an aluminummatrix.

The strip may then be rolled and cast into bearing blanks in theabove-described manner to obtain my improved bearing properties. Ingeneral, the soft metal(s) will form a minor portion, less than about toby weight, of the aluminum based alloy. Preferably, lead is employed asthe principal soft metal in amounts of about one to ten percent byweight of the aluminum alloy.

While my invention has been described in terms of a preferred embodimentthereof it is recognized that other forms could be adapted by oneskilled in the art and, therefore, the scope of my invention should beconsidered limited only by the following claims.

What is claimed is:

1. A bearing blank in the form of a rolled strip of metal comprising amajor portion of aluminum and a minor portion of a soft metal, said softmetal being prescut as a dispersion of generally flat elongatedplatelets in an aluminum matrix, said platelets being generally parallelto a major fiat surface of said bearing blank and the longest dimensionof said platelets being transverse to an intended direction of rotationof a journal member adapted to mate with a bearing formed from saidbearing blank.

2. A bearing blank in the form of a rolled strip of metal comprising amajor portion of aluminum and a minor portion of a soft metal selectedfrom the group consisting of lead, cadmium and bismuth, said soft metalbeing present as a dispersion of generally flat elongated platelets inan aluminum matrix, said platelets being generally parallel to a majorflat surface of said bearing blank and the longest dimension of saidplatelets being transverse to an intended direction of rotation of ajournal member adapted to mate with a bearing formed from said bearingblank.

5. A bearing blank in the form of a rolled cast strip in which at leasta portion of said bearing blank is a layer of aluminum alloy containinga minor portion, up to about 20% by weight, of a soft metal selectedfrom the group consisting of lead, cadmium and bismuth, said soft metalbeing present as a dispersion of generally flat elongated platelets inan aluminum matrix, said platelets being generally parallel to a majorfiat surface of said bearing blank and the longest dimension of saidplatelets being transverse to an intended direction of rotation of ajournal member adapted to mate with a bearing formed from said bearingblank.

4. A rolled cast bearing blank strip in which at least a portion of saidstrip is a layer of aluminum alloy containing about 1% to 10% by weightlead, said lead being present as a dispersion of generally flatplatelets in an aluminum matrix, said lead platelets being generallyparallel to a major flat surface of said bearing blank strip and thelongest dimension of said platelets being transverse to an intendeddirection of rotation of a journal member adapted to mate with a bearingformed from said bearing blank.

5. A composite sleeve bearing comprising a rolled aluminum alloy bearinglayer and a backup layer integrally bonded to one side of said bearinglayer, said bearing layer comprising a major portion of aluminum and aminor portion, up to about 20% by Weight, of a soft metal selected fromthe group consisting of lead, cadmium and bismuth, said soft metal beingpresent as a dispersion of generally flat, elongated platelets in analuminum matrix, said platelets being generally parallel to the bearingsurface of said bearing layer and the longest dimension of saidplatelets being transverse to an intended direction of rotation of ajournal member adapted to mate with said bearing.

6. A composite sleeve bearing comprising a rolled aluminum alloy bearinglayer and a steel backup layer integrally bonded to one side of saidbearing layer, said bearing layer being an aluminum alloy containingabout 1% to 10% by weight lead, said lead being present as a dispersionof generally fiat platelets in an aluminum matrix, said lead plateletsbeing generally parallel to the bearing surface of said bearing layerand the longest dimension of said platelets being transverse to anintended direction of rotation of a journal member adapted to mate withsaid bearing.

References Cited UNITED STATES PATENTS 3,221,392 12/1965 Gould et al.29-1912 X 2,537,591 1/1951 Klein 29191.2 X 2,815,567 12/1957 Gould etal. 29-1912 X 3,410,331 11/1968 Miller et al. 16451 2,971,248 2/1961Kingsley et al. 308-239 X MARTIN P. SCHWADRON, Primary Examiner B.GROSSMAN, Assistant Examiner

